Shows already owned games.

I believe it is caused because the Steam API does not filter them properly, so you have to do it yourself with some of them, specially Game of the year Editions, Complete Editions, etc. Also, you should keep your profile synced and up to date.

I think something Valve changed recently regarding removed games resulted in Steamgifts not being able to see if you already own them, so you will have to hide those giveaways manually.

I have the same problem with sam & max season one. Won it a few days ago but the giveaways for this game are still visible for me. Syncing didn´t help so i blocked it manually. It was the first time i encountered that problem.